1. Field of the Invention
The invention is directed to a process for coating elongated metallic material, particularly strip or wire, with multiple layers by applying different layers of metallic coating materials while the material to be coated travels continuously through an installation having a plurality of dip baths with molten coating materials.
2. Description of Prior Art
Processes of the type described above are known (GB 15 74 814) and are used to improve surfaces, in particular to improve the resistance of metal strips or metal wires to corrosion. The coating materials which are applied in multiple layers, e.g. a first layer of aluminum/5-12% silicon and a second layer of aluminum, also improve the deformation properties of the strip and the adhesive strength and corrosion resistance of the coating material. In another known process (DE-A1-31 24 161), a steel strip whose surface has been prepared is guided through two adjacent tanks one after the other. The first tank contains a zinc bath and the second contains an alloy bath and the bath temperatures of both tanks can be regulated. The accompanying device provides means and steps for introducing the strip into the tank, deflecting it therein and then guiding it out of the tank and into and out of the next tank. In a known manner, wipers remove excess coating material from the coated strip as it leaves the second tank and, at the same time or subsequently, the strip is brought to a temperature at which the coating material solidifies in its entirety. In this way the surface quality and adhesive capacity of the coating is improved.
A disadvantage in the known process and in the known device consists in that it is not possible to exert a directed influence on the diffusion process between the molten coating material and steel strip or to bring optimal temperature conditions into precise accord during the application of the first and second coating layers. As a result of the arrangement of adjacent tanks with required deflecting means for the strip, restrictions are imposed on the minimum coating time since it is impossible to guide the material to be coated on a direct path. Moreover, in the given arrangement of the installation, contamination of the dip baths by iron is inevitable so that the quality of the coated material is impaired.
A device for guiding cast bar material in a straight line through an individual, vertically arranged tank in which the level of the dip bath is adjustable is known from DE-A-36 38 249.